As a turbocharger installed in a vehicle or the like, a turbocharger of a twin-scroll type is known in which a passage between a turbine housing inlet and a leading edge of turbine rotor blades is separated into a front side (an exhaust gas outlet side) and a rear side (a bearing housing side) so as to avoid interference with the exhaust gas of a multicylinder engine and also to utilize pulsation of the exhaust gas of the engine (dynamic pressure). A twin-scroll turbocharger of this type is disclosed in Patent Literatures 1 and 2.
An example construction of the conventional turbocharger of twin-scroll type which is disclosed in Patent Literature 2 is now described in reference to FIG. 3 and FIG. 4. In FIG. 3, a turbine housing 102 of the turbocharger of the twin-scroll type has a scroll passage for the exhaust gas inside. A partition wall 104 protruding in the passage separates a scroll passage 106 on the front side and a scroll passage 108 on the rear side.
A turbine shaft 110 and a turbine wheel integrally formed with the turbine shaft 110 are arranged in a center part of the turbocharger 100. A plurality of turbine rotor blades 114 are integrally formed around the turbine wheel 112 in a radial fashion.
As shown in FIG. 4, the scroll passages 106, 108 are formed in a scroll shape. The exhaust gas e flows in the scroll passages 106, 108 from the outside toward the inside in the radial direction, and then enters the turbine rotor blades 114 from an outlet opening 116 so as to rotate the turbine wheel 112. Then, the exhaust gas e passes through an outlet casing 118 and is drained.
A bearing housing 120 is arranged next to the turbine housing 102. The turbine housing 102 is provided with a connection flange 122 in contraposition to the bearing housing 120 so that the bearing housing 120 and the turbine housing 102 are coupled to each other. The turbine housing 102 and the bearing housing 120 are fixed normally by connecting the connection flange 122 and a connection flange (not shown) provided in the bearing housing 120 by means of a coupling of a ring shape.
Near an outlet flange 124 of the turbine housing 102, a wastegate valve 126 is provided for controlling a supercharging pressure of the turbocharger 100 at a setting pressure or below. By allowing a part of the exhaust gas flowing in the front scroll passage 106 and the rear scroll passage 108 to exit the exhaust gas exit from the wastegate valve 126, the supercharging pressure of the turbocharger 100 is controlled not more than the setting value.
According to the above structure, the exhaust gas e exhausted from the engine (not shown) enters the turbine rotor blades 116 via the scroll passages 106, 108, thereby rotating the turbine wheel 110. The rotation of the turbine wheel 110 rotates a compressor wheel (not shown) coupled to the turbine shaft 110. This generates a flow of the intake air and the intake air is supplied to the combustion cylinder. In the multicylinder engine, by dividing the exhaust gas e exhaust from the combustion cylinder to two scroll passages 106, 108 so as to suppressing the interference of the multicylinder engine with the exhaust gas energy as well as to improve the rotation efficiency of the turbine shaft 110 by using the pulsation of the exhaust gas.
In this manner, the rotation of the turbine in a low-speed rotation range is started early without decreasing A/R and thus it is possible to improve a response speed of the turbocharger in the low-speed rotation range as well as the output of the engine.